A known vehicle cooling device is shown in FIG. 5. As shown in FIG. 5, a vehicle cooling device 51 includes a water pump 55 for discharging the cooling water to an engine 53 side and a thermostat 54 for controlling the valve opening in accordance with the temperature of the cooling water. The vehicle cooling device 51 maintains the water temperature of the engine 53 at a predetermined temperature by the thermostat 54 for controlling the flow volume balance of the cooling water passing through the radiator 52 and the cooling water directly provided from the engine 53.
As shown in FIG. 6, a housing 59 of the thermostat 54 includes a first conduit 58 where the cooling water from a radiator outlet 52a of the radiator 52 flows. An intake passage 55a of the water pump 55 and a second conduit 56 where the cooling water from the engine outlet 53a of the engine 53 flows are connected to the thermostat 54. The housing 59 accommodates a water temperature sensing portion 60a of a thermo element 60. The thermo element 60 is attached with a main valve 61 and a bypass valve 62. The main valve 61 and the bypass valve 62 control the opening and closing of the first conduit 58 and the second conduit 56.
According to the construction of known vehicle cooling devices described in Japanese Utility Patent Laid-Open Publication No. S60-131625 and Japanese Utility Patent Laid-Open Publication No. S62-85777, a flow directing wall 63 for directing and introducing the cooling water from the second conduit 56 to the water temperature sensing portion 60a is formed between the second conduit 56 and the intake passage 55a in the housing 59. Thus, the cooling water from the second conduit 56 mixed with the cooling water from a heater conduit 57 and the first conduit 58 contacts the water temperature sensing portion 60a before flowing to the water pump 55 side, and the water temperature of the cooling water can be controlled precisely by the thermostat 54.
The thermostat 54 with the foregoing construction supplies the cooling water from the radiator 52 to the engine 53 via the first conduit 58. Because the cooling water is at the low temperature at the engine start, the cooling water returns to the engine 53 via the heater conduit 57 and the water pump 55. When the cooling water reaches a predetermined temperature after the warming up, the wax in the thermo element 60 expands so that a piston 64 projects. In other words, the piston 64 projects in accordance with the temperature of the cooling water. The valve opening of the main valve 61 increases in accordance with the increase of the projection amount of the piston 64 to open the first conduit 58 and to decrease the valve opening of the bypass valve 62. Accordingly, the cooling water cooled at the radiator 52 flows into the water pump 55 in accordance with the distribution ratio of respective conduits 56–58 by the valve openings of the main valve 61 and the bypass valve 62 to be introduced to the engine inlet 53b of the engine 53. The cooling water derived from the engine 53 is distributed to the radiator 52 (i.e., first conduit 58), the second conduit 56, and the heater conduit 57. When the projection amount of the piston 64 assumes the predetermined value, the second conduit 56 is closed.
Notwithstanding, with the construction of the known vehicle cooling device, a portion of the water pump 55 contacting the intake passage 55a is positioned at an external peripheral portion (i.e., external radial side of the main valve 61) of the housing 59. Thus, the water pressure and the flow force to the intake passage 55a side affects relative to the movable portion including the main valve 61 by the introduction of the cooling water by actuating the water pump 55. Accordingly, the partial wear is generated at a sealing surface 61a of the main valve 61, at a valve supporting portion 65 of the main valve 61, and at an external cylinder portion of the thermo element 60, which makes it difficult to increase the longevity of the thermostat 54.
In case the thermostat 54 with the known construction is used, the flow directing wall 63 is required for controlling the water temperature of the cooling water. However, the flow directing wall 63 blocks the smooth flow of the cooling water, which causes the increase of the water flow resistance in the housing 59. In other words, the mixture of the cooling water from the conduits 56–58 in the housing 59 causes the contradiction between the optimum water temperature controllability and the water flow resistance at the cooling system element characteristic. Accordingly, it is required to direct the cooling water by increasing the driving force of the water pump 55. In addition, in case a portion with large water flow resistance exists at the intake side of the water pump 55, the cavitation is likely to be generated, which declines the durability of the water pump 55.
A need thus exists for a vehicle cooling device which enables to increase the longevity of a thermostat, to reduce the driving force of a water pump, and to increase the durability.